We do not have all the data. We do not know if Jonah said those eight words more than once or if he repeated them as he trudged along 1/3 of the way into Nineveh. Neither do we know if he went out of the city the same way or went out another gate.
However, based on Jonah’s attitude in the first couple of chapters, it seems to me that it is possible that Jonah walked into the city 1/3 of the way, said his eight words, and turned around and walked out.
This seems to highlight the power of God to deal with an issue regardless of the commitment or passion of the instrument of His grace.
God does not need eloquence. He does not need overwhelming effort. He does not need a full commitment or passion. He can use our halting, 1/3 hearted, stumbling, and minimalist effort to create a revival and change the hearts of a city.
This is not about our effort. It is about His power to change the hearts of people.